Optical Wavelength Conversion Element Containing Ionic Liquid, And Article Equipped With Said Optical Wavelength Conversion Element

Abstract

There is provided an optical wavelength conversion element with a good temporal stability and such a high optical wavelength conversion efficiency that the element is viable even under sunlight or similar, low intensity light. Owing to these properties, the element is suited for use in solar cells, photocatalysts, photocatalytic hydrogen and oxygen generating devices, photon upconversion filters, and like articles. The optical wavelength conversion element is visually homogeneous and transparent and produced by dissolving and/or dispersing in an ionic liquid (C) a combination of organic photosensitizing molecules (A) and organic light-emitting molecules (B) that exhibits triplet-triplet annihilation. When the ionic liquid (C) is washed with a volume of ultrapure water that is 9 times as much as the volume of the ionic liquid (C), the water resulting from the washing has a pH larger than 5.

1 . A visually homogeneous and transparent optical wavelength conversion element comprising: a combination of organic photosensitizing molecules (A) and organic light-emitting molecules (B) that exhibits triplet-triplet annihilation; and an ionic liquid (C), the element being produced by dissolving and/or dispersing the combination in the ionic liquid (C), wherein water resulting from washing the ionic liquid (C) with a volume of ultrapure water that is 9 times as much as the volume of the ionic liquid (C) has a pH larger than 5. 
     
     
         2 . The optical wavelength conversion element according to  claim 1 , wherein the organic photosensitizing molecules (A) have a local maximum absorption wavelength of from 500 nm to 700 nm. 
     
     
         3 . The optical wavelength conversion element according to  claim 1 , wherein the organic photosensitizing molecules (A) have a structure containing no metal. 
     
     
         4 . The optical wavelength conversion element according to  claim 1 , wherein the organic photosensitizing molecules (A) are a compound of general formula (1) 
       
         
           
           
               
               
           
         
         where each of R 1  to R 5  is independently any substituent including a hydrogen atom, adjacent substituents (R 1  and R 2 , R 2  and R 4 , R 1  and R 3 , and R 3  and R 4 ) may be joined together to form a five- or six-membered ring having any substituent including a hydrogen atom, and R 6  is a halogen atom, a C 1 -C 5  alkyl group that may contain a substituent, or a C 1 -C 5  alkoxyl group that may contain a substituent. 
       
     
     
         5 . The optical wavelength conversion element according to  claim 4 , wherein each of R 1  to R 5  in general formula (1) is independently a hydrogen atom, a halogen atom, a C 1 -C 4  aliphatic hydrocarbon group that may contain a substituent, a phenyl group that may contain a substituent, a phenoxy group that may contain a substituent, a thienyl group that may contain a substituent, a thienoxy group that may contain a substituent, a 2-carboxylethenyl group of general formula (2) 
       
         
           
           
               
               
           
         
       
       or 
       a 2-carboxyl-2-cyanoethenyl group of general formula (3) 
       
         
           
           
               
               
           
         
       
     
     
         6 . The optical wavelength conversion element according to  claim 1 , wherein the organic photosensitizing molecules (A) are a compound of general formula (4) 
       
         
           
           
               
               
           
         
         where each of R 1  and R 4  is independently a C 1 -C 3  alkyl group that may contain a substituent, each of R 2  and R 3  is independently a hydrogen atom, a bromine atom, or an iodine atom, either one or both of R 2  and R 3  is/are a bromine atom or an iodine atom, and R 5  is a phenyl group that may contain a substituent. 
       
     
     
         7 . The optical wavelength conversion element according to  claim 1 , further comprising a gelator (D). 
     
     
         8 . The optical wavelength conversion element according to  claim 7 , wherein the element is in a gel state. 
     
     
         9 . The optical wavelength conversion element according to  claim 7 , wherein the gelator (D) is an ionic gelator. 
     
     
         10 . The optical wavelength conversion element according to  claim 7 , wherein the gelator (D) is a nonionic polymer. 
     
     
         11 . A solar cell comprising the optical wavelength conversion element according to  claim 1 . 
     
     
         12 . A photocatalyst comprising the optical wavelength conversion element according to  claim 1 . 
     
     
         13 . A photocatalytic hydrogen and oxygen generating device comprising the optical wavelength conversion element according to  claim 1 . 
     
     
         14 . A photon upconversion filter converting light of relatively long wavelengths to light of relatively short wavelengths,
 the filter comprising:   the optical wavelength conversion element according to  claim 1 ; and   a cell,   wherein the optical wavelength conversion element is sealed in the cell.